Lifting platforms for motor vehicles are typically available in two standard designs. In the first configuration which is operated with medium or low hydraulic pressure, the lifting piston also forms the supporting piston. The cylinder which is connected to an oil supply is arranged in a pit and its upper end is mounted on a stationary supporting structure. The hoisting element is formed by a trunk piston that projects with its lower section into the oil-filled interior of the cylinder, and its piston rod has the supporting elements for the motor vehicle on the upper end. To guide and seal the trunk piston rod, a relatively long guide bushing is provided in the top end section of the cylinder, and its friction surface is subjected to forced lubrication by entrained oil with each ejection movement of the piston rod. In this design a relatively low surface wear on the piston road and especially the guide bushings is achieved due to the forced lubrication in the area of the guide bushing. However, disadvantages are high cost of production plus the size of the individual parts required such as pumps, valves, etc. Such a lifting platform in a two-cylinder design is described in publication DAT 80, page 4.
Lifting platforms of the second structure are operated with hydraulic high pressure and have a relatively narrow high-pressure cylinder on the inside that assumes the actual lifting work, and they have an outer supporting piston or supporting tube. With a single cylinder lifting platform described in publication DAT 80, page 3, a high-pressure cylinder that accomplishes the lifting work is coaxially positioned in the interior of the supporting tube. The hollow piston rod is attached with its lower end to the base plate of the pit and contains an internal pressurized oil line that opens through valves into the pressure space limited by the piston attached to the upper end of the piston rod on the one end, and on the other end it is limited by the cover plate of the cylinder. The supporting tube surrounds the high-pressure cylinder with a radial distance and is guided in a relatively long guide tube which is attached to the side wall or the cover frame of the pit. Two friction surfaces with an axial distance between them are provided on the guide tube, but they do not necessarily receive forced lubrication. The high-pressure cylinder is connected to a supply unit through pipelines arranged next to the supporting tube in the pit and connected to the internal pressurized oil line that runs in the hollow piston beneath the bottom plate. This known high-pressure lifting platform is less expensive to manufacture because of its compact individual parts. Because of lack of forced lubrication of the friction surfaces between the guide tube and the outside surface of the cylinder, however, the guide tube is susceptible to wear. Built-in lubrication chambers or droplet lubrication can improve the wear phenomena but are effective only for a limited period of time.